Studies on Heme Oxygenase 1 During Erythroid Differentiation

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 4254-4254
Author(s):  
Daniel Garcia Santos ◽  
Jesse Eisenberg ◽  
Matthias Schranzhofer ◽  
Prem Ponka
Keyword(s):  
Aminolevulinic Acid ◽  
Conflicts Of Interest ◽  
Tissue Injury ◽  
Erythroid Differentiation ◽  
The Body ◽  
Cellular Damage ◽  
Erythroid Cell ◽  
Heme Oxygenase 1 ◽  
Erythroid Cells ◽  
Murine Erythroleukemia

Abstract Abstract 4254 Heme is indispensable for the function of all aerobic cells as a prosthetic group of innumerable proteins. However, “free heme” (uncommitted) can initiate the formation of free radicals and cause lipid peroxidation, which can lead to cellular damage and tissue injury. Therefore, the rate of heme biosynthesis and catabolism must be well balanced by tight control mechanisms. The highest amounts of organismal heme (75-80%) are present in circulating red blood cells (RBC), whose precursors synthesize heme with rates that are at least one order of magnitude higher (on the per cell basis) than those in the liver – the second most active heme producer in the body. The degradation of heme is exclusively carried out by heme oxygenases 1 and 2 (HO1 and HO2), which catalyze the rate-limiting step in the oxidative degradation of heme. Although the heme-inducible HO isoform, HO1, has been extensively studied in hepatocytes and many other non-erythroid cells, virtually nothing is known about the expression of HO1 in developing RBC. Similarly, it is unknown whether HO1 plays any role in erythroid cell development under physiological or pathophysiological conditions. Using both a murine erythroleukemia cell line (MEL) and primary erythroid cells isolated from mouse fetal livers, we have demonstrated that during erythroid differentiation HO1 is up-regulated at both mRNA and protein levels. This increase in HO1 can be prevented by succinylacetone (SA), an inhibitor of heme synthesis that blocks 5-aminolevulinic acid dehydratase. These data suggest that in developing RBC, in addition to the continuous assembly of heme with globin chains, there is an increase in levels of uncommitted heme, which upregulates HO1 expression. Additionally, we have shown that down-regulation of HO1 via siRNA increased hemoglobinization in differentiating MEL cells. In contrast, induction of HO1 expression by NaAsO2 reduced the hemoglobinization of MEL cells. This effect could be reversed to control levels by the addition of HO1 inhibitor tin-protophorphyrin (SnPP). These results show that in differentiating erythroid cells the balance between levels of heme and HO1 have to be tightly regulated to maintain hemoglobinization at appropriate levels. Our results lead us to propose that disturbances in HO1 expression could play a role in some pathophysiological conditions such as thalassemias. Disclosures: No relevant conflicts of interest to declare.

Investigation of the Role of Heme Oxygenase 1 During Erythroid Differentiation.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1997-1997
Author(s):  
Daniel Garcia dos Santos ◽  
Jesse Eisenberg ◽  
Matthias Schranzhofer ◽  
Jose Artur Bogo Chies ◽  
Prem Ponka
Keyword(s):  
Red Blood Cells ◽  
Blood Cells ◽  
Conflicts Of Interest ◽  
Tissue Injury ◽  
Physiological Mechanism ◽  
Erythroid Differentiation ◽  
The Body ◽  
Erythroid Cell ◽  
Heme Oxygenase 1 ◽  
Erythroid Cells

Abstract Abstract 1997 Poster Board I-1019 Heme is a complex of iron with protoporphyrin IX that is essential for the function of all aerobic cells. However, if left unguarded, non-protein-bound heme promotes free radical formation, resulting in cell damage and tissue injury. The highest amounts of organismal heme (75-80%) are present in circulating red blood cells (RBC) whose precursors synthesize heme with rates that are at least 1 order of magnitude higher than those in the liver (on the per cell basis), which is the second most active heme producer in the body. The only physiological mechanism of heme degradation is by heme oxygenases (HO1 and HO2) that catalyze the rate-limiting step in the oxidative degradation of heme and are, therefore, involved in the control of cellular heme levels. Red blood cells contain the majority of heme destined for catabolism; this process takes place in splenic and hepatic macrophages following erythrophagocytosis of senescent RBC. Although the heme-inducible HO isoform, HO1, has been extensively studied in hepatocytes and many other non-erythroid cells, virtually nothing is known about the expression of HO1 in developing RBC. Similarly, it is unknown whether HO1 plays any role in erythroid cell development under physiological or pathophysiological conditions. In this study we have shown that HO1 protein is expressed in uninduced murine erythroleukemic (MEL) cells and that its levels, somewhat surprisingly, do not decrease during DMSO-induced erythroid differentiation. Moreover, we demonstrated that heme significantly induces HO1 in both uninduced and induced MEL cells. Additionally, we investigated the effect of sodium arsenite (NaAsO2), HO1 inducer, on heme and iron metabolism in MEL cells induced to erythroid differentiation. MEL cells treated with NaAsO2 displayed a significant reduction in globin expression and increased ferritin levels. Moreover, NaAsO2treatment decreased levels of transferrin receptor in cell membranes. These effects triggered by NaAsO2 could be prevented by the addiction of tin-protophorphyrin (SnPP), HO1 activity inhibitor. Using a siRNA specifically targeting HO1, we observed an increase in globin expression together with a small decrease in the expressin of ferritin in DMSO-induced MEL cells. These results suggest that an as yet unknown mechanism exists to protect heme against endogenous HO1 action during erythroid differentiation. In summary, our results showing that NaAsO2-induced HO1 in erythroid cells cause a defect in erythroid differentiation suggest that HO1 could play a role in some pathophysiological conditions such as thalassemias. Disclosures: No relevant conflicts of interest to declare.

The Role of Heme Oxygenase 1 in Erythroid Differentiation.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3847-3847
Author(s):  
Daniel Garcia dos Santos ◽  
Matthias Schranzhofer ◽  
Jose Artur Bogo Chies ◽  
Prem Ponka
Keyword(s):  
Red Blood Cells ◽  
Blood Cells ◽  
Tissue Injury ◽  
Erythroid Differentiation ◽  
The Body ◽  
Erythroid Cell ◽  
Heme Oxygenase 1 ◽  
Transferrin Receptors ◽  
Erythroid Cells ◽  
Wild Type

Abstract Heme is a complex of iron with protoporphyrin IX that is essential for the function of all aerobic cells. However, if left unguarded, non-protein-bound heme promotes free radical formation, resulting in cell damage and tissue injury. The highest amounts of organismal heme (75–80%) are present in circulating red blood cells (RBC) whose precursors synthesize heme with rates that are at least 1 order of magnitude higher than those in the liver (on the per cell basis), which is the second most active heme producer in the body. The only physiological mechanism of heme degradation is performed by heme oxygenases (HO1 and HO2), which catalyze the rate-limiting step in the oxidative degradation of heme and are, therefore, involved in the control of cellular heme levels. Red blood cells contain the majority of heme destined for catabolism; this process takes place in splenic and hepatic macrophages following erythrophagocytosis of senescent RBC. Although the heme-inducible HO isoform, HO1, has been extensively studied in hepatocytes and many other non-erythroid cells, virtually nothing is known about the expression of HO1 in developing RBC. Similarly, it is unknown whether HO-1 plays any role in erythroid cell development under physiological or pathophysiological conditions. In this study we have shown that HO1 protein is expressed in uninduced murine erythroleukemic (MEL) cells and that its levels, somewhat surprisingly, do not decrease during DMSO-induced erythroid differentiation. Moreover, we demonstrated that heme significantly induces HO1 in both uninduced and induced MEL cells. Additionally, we investigated the effect of overexpressed HO1 on heme and iron metabolism in stably transfected MEL cells (MEL-HO1) and their non-transfected counterparts. Compared to wild type cells, DMSO-treated MEL-HO1 cells displayed a reduction in heme stability (measured by the incorporation of 59Fe into heme) in addition to impairment of erythroid differentiation. Moreover, although wild type and transfected cells expressed similar levels of transferrin receptors in the uninduced state, MEL-HO1 cells, as compared to wild type MEL cells, showed only a small increase in transferrin receptors upon treatment with DMSO. Finally, we measured apoptosis using annexin-V and observed an increase in the number of apoptotic cells in HO1 transfectants, but not in wild type MEL cells. These results suggest that an as yet unknown mechanism exists to protect heme against endogenous HO1 action during physiological erythroid differentiation. In addition, our results showing that high levels of HO1 in erythroid cells cause heme catabolism and a defect in erythroid differentiation raise the possibility that HO1 could play a role in some pathophysiological conditions such as unbalanced globin synthesis in thalassemias.

LSD1 Plays an Important Role in GATA Switch during Erythroid Differentiation

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 4846-4846
Author(s):  
Yue Jin ◽  
Yidi Guo ◽  
Dongxue Liang ◽  
Yue Li ◽  
Zhe Li ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Conflicts Of Interest ◽  
Es Cells ◽  
Regulatory Element ◽  
Erythroid Differentiation ◽  
Erythroid Cell ◽  
Erythroid Cells ◽  
Hematopoietic Stem ◽  
Mouse Es Cells ◽  
Murine Erythroleukemia

Abstract GATA factors play important role in hematopoiesis. In particular, GATA2 is critical for maintenance of hematopoietic stem and progenitor cells (HS/PCs) and GATA1 is required for erythropoiesis. GATA1 and GATA2 are expressed in reciprocal patterns during erythroid differentiation. It was shown that GATA1 occupied the -2.8Kb regulatory element and mediated repression of the GATA2 promoter in terminally differentiating erythroid cells. However, the detailed molecular mechanisms that control the enhancer/promoter activities of the GATA2 gene remain to be elucidated. In this report, we found that LSD1 and TAL1 co-localize at GATA2 1S promoter through ChIP and double-ChIP assays in murine erythroleukemia (MEL) cells. To further test whether LSD1 and its mediated H3K4 demethylation is important for repression of the GATA2 gene during erythroid differentiation, we silenced LSD1 expression in both MEL cells and mouse ES cells using retrovirus mediated shRNA knockdown and induced them to differentiate into erythroid cells with DMSO and EPO, respectively. GATA2 expression was elevated while the level of GATA1 was repressed by RT-qPCR. Furthermore, consistent with the GATA witch hypothesis, ChIP analysis revealed that the levels of H3K4me2 were increased at the GATA2 1S promoter.  In addition, knock-down of LSD1 in MEL cells results in inhibition of erythroid cell differenciation and attenuation of MEL cell proliferation and survival. Thus, our data reveal that LSD1 involved in control of terminal erythroid differentiation by regulating GATA switch. The LSD1 histone demethylase complex may be recruited to the GATA2 1S promoter by interacting with TAL1. The H3K4 demethylation activity of LSD1 leads to downregulation of the active H3K4m2 mark at the GATA2 promoter that alters chromatin structure and represses transcription of the GATA2 genes. Disclosures: No relevant conflicts of interest to declare.

Klf1 Regulatory Networks in Primary Erythroid Cells.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1462-1462
Author(s):  
Michael Tallack ◽  
Thomas Whitington ◽  
Brooke Gardiner ◽  
Eleanor Wainwright ◽  
Janelle Keys ◽  
...  
Keyword(s):  
Regulatory Networks ◽  
Conflicts Of Interest ◽  
Fetal Liver ◽  
Es Cells ◽  
Erythroid Differentiation ◽  
Erythroid Cell ◽  
Gene Promoters ◽  
Erythroid Cells ◽  
Red Cell Membrane ◽  
Sequencing Platform

Abstract Abstract 1462 Poster Board I-485 Klf1/Eklf regulates a diverse suite of genes to direct erythroid cell differentiation from bi-potent progenitors. To determine the local cis-regulatory contexts and transcription factor networks in which Klf1 works, we performed Klf1 ChIP-seq using the SOLiD deep sequencing platform. We mapped more than 10 million unique 35mer tags and found ∼1500 sites in the genome of primary fetal liver erythroid cells are occupied by endogenous Klf1. Many reside within well characterised erythroid gene promoters (e.g. b-globin) or enhancers (e.g. E2f2 intron 1), but some are >100kb from any known gene. We tested a number of Klf1 bound promoter and intragenic sites for activity in erythroid cell lines and zebrafish. Our data suggests Klf1 directly regulates most aspects of terminal erythroid differentiation including synthesis of the hemoglobin tetramer, construction of a deformable red cell membrane and cytoskeleton, bimodal regulation of proliferation, and co-ordination of anti-apoptosis and enucleation pathways. Additionally, we suggest new mechanisms for Klf1 co-operation with other transcription factors such as those of the gata, ets and myb families based on over-representation and spatial constraints of their binding motifs in the vicinity of Klf1-bound promoters and enhancers. Finally, we have identified a group of ∼100 Klf1-occupied sites in fetal liver which overlap with Klf4-occupied sites in ES cells defined by Klf4 ChIP-seq. These sites are associated with genes controlling the cell cycle and proliferation and are Klf4-dependent in skin, gut and ES cells, suggesting a global paradigm for Klfs as regulators of differentiation in many, if not all, cell types. Disclosures No relevant conflicts of interest to declare.

Heme Oxygenase 1 Plays An Unexpected Role During Erythroid Differentiation

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 344-344
Author(s):  
Daniel Garcia Santos ◽  
Matthias Schranzhofer ◽  
José Artur Bogo Chies ◽  
Prem Ponka
Keyword(s):  
Red Blood Cells ◽  
Heme Oxygenase ◽  
Blood Cells ◽  
Erythroid Differentiation ◽  
Heme Biosynthesis ◽  
Erythroid Cell ◽  
Heme Oxygenase 1 ◽  
Erythroid Cells ◽  
Wild Type ◽  
Protein Levels

Abstract Abstract 344 Red blood cells (RBC) are produced at a rate of 2.3 × 106 cells per second by a dynamic and exquisitely regulated process known as erythropoiesis. During this development, RBC precursors synthesize the highest amounts of total organismal heme (75–80%), which is a complex of iron with protoporphyrin IX. Heme is essential for the function of all aerobic cells, but if left unbound to protein, it can promote free radical formation and peroxidation reactions leading to cell damage and tissue injury. Therefore, in order to prevent the accumulation of ‘free' heme, it is imperative that cells maintain a balance of heme biosynthesis and catabolism. Physiologically, the only enzyme capable of degrading heme are heme oxyganase 1 & 2 (HO). Red blood cells contain the majority of heme destined for catabolism; this process takes place in splenic and hepatic macrophages following erythrophagocytosis of senescent RBC. Heme oxygenase, in particular its heme-inducible isoform HO1, has been extensively studied in hepatocytes and many other non-erythroid cells. In contrast, virtually nothing is known about the expression of HO1 in developing RBC. Likewise, it is unknown whether HO1 plays any role in erythroid cell development under physiological or pathophysiological conditions. Using primary erythroid cells isolated from mouse fetal livers (FL), we have shown that HO1 mRNA and protein are expressed in undifferenetiated FL cells and that its levels, somewhat surprisingly, increase during erythropoietin-induced erythroid differentiation. This increase in HO1 can be prevented by succinylacetone (SA), an inhibitor of heme synthesis that blocks 5-aminolevulinic acid dehydratase, the second enzyme in the heme biosynthesis pathway. Moreover, we have found that down-regulation of HO1 via siRNA increases globin protein levels in DMSO-induced murine erythroleukemic (MEL) cells. Similarly, compared to wild type mice, FL cells isolated from HO1 knockout mice (FL/HO1−/−) exhibited increased globin and transferrin receptor levels and a decrease in ferritin levels when induced for differentiation with erythropoietin. Following induction, compared to wild type cells, FL/HO1−/− cells showed increased iron uptake and its incorporation into heme. We therefore conclude that the normal hemoglobinization rate appears to require HO1. On the other hand, MEL cells engineered to overexpress HO1 displayed reduced globin mRNA and protein levels when induced to differentiate. This finding suggests that HO1 could play a role in some pathophysiological conditions such as unbalanced globin synthesis in thalassemias. Disclosures: No relevant conflicts of interest to declare.

Heme Oxygenase 1 Plays a Role In The Pathophysiology Of β-Thalassemia

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 3449-3449 ◽  
Author(s):  
Daniel Garcia Santos ◽  
Marc Mikhael ◽  
Stefano Rivella ◽  
Monika Horvathova ◽  
Prem Ponka
Keyword(s):  
Heme Oxygenase ◽  
Conflicts Of Interest ◽  
Erythroid Differentiation ◽  
Thalassemia Major ◽  
Severe Form ◽  
Cellular Damage ◽  
Heme Oxygenase 1 ◽  
Globin Chains ◽  
Thalassemia Minor ◽  
Free Heme

Abstract Thalassemias are a heterogeneous group of red blood cell disorders ranging from a clinically severe phenotype requiring life-saving transfusions (thalassemia major) to a relatively moderate symptomatic disorder, sometimes requiring transfusions (thalassemia intermedia). Thalassemia minor, the least severe form of the disorder, is characterized by minimal to mild symptoms. While thalassemia minor and intermedia are vastly more prevalent than thalassemia major, the latter is often fatal when not treated. Though considered a major cause of morbidity and mortality worldwide, there is still no universally available cure for this severe form of thalassemia. A reason for this is at least in part due to the lack of full understanding of pathophsyiology of thalassemia. The underlying cause of pathology in thalassemia is the premature apoptotic destruction of erythroblasts causing ineffective erythropoeisis. Normally, the assembly of adult hemoglobin (consisting of a tetramer of two α- and two β-globin chains) features a very tight coordination of α- and β-globin chain synthesis. However, in β-thalassemia, β-globin synthesis is decelerated causing α-globin accumulation; while in α-thalassemia the opposite scenario occurs. Unpaired globin chains that accumulate in thalassemic erythroblasts are bound to heme. In addition, in β-thalassemia an erythroid specific protease destroys excess α-globin chains, likely leading to the generation of a pool of “free” heme in erythroblasts. “Free” heme is toxic, but this toxicity will likely be augmented, if heme oxygenase 1 (HO-1) can release iron from heme. To date, virtually no information about the expression of HO-1 in erythroblasts has been produced; however, we have recently provided unequivocal evidence that this enzyme is present in several model erythroid cells1. Based on this novel and important finding, we hypothesize that in β-thalassemic erythroblasts HO-1 mediated release of iron from heme is the major culprit responsible for cellular damage. To test this hypothesis we exploited the mouse model of β-thalassemia, th3/+. Thus far, our data indicates that HO-1 expression is increased in liver, spleen and kidney of β-thalassemic mice compared to wild type mice. Importantly, we observed that Epo-mediated erythroid differentiation of fetal liver (FL) cells isolated from β-thalassemic fetuses, display increased levels of HO-1 as well as decreased phosphorylated eiF2-α. These results indicate that β-thalassemic erythroblasts have inappropriately high levels of unbound heme that is continuously degraded by HO-1. Further research is needed to determine whether HO-1 liberated iron is responsible for the damage of β-thalassemic erythroblasts. 1Garcia Santos D, Schranzhofer M, Bogo Chies JA, Ponka P. Heme Oxygenase 1 plays an unexpected role during erythroid differentiation. Blood (ASH Annual Meeting Abstracts) 118: 344, 2011. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Expression of ferrochelatase mRNA in erythroid and non-erythroid cells

1993 ◽  
Vol 292 (2) ◽  
pp. 343-349 ◽  
Author(s):  
R Y Y Chan ◽  
H M Schulman ◽  
P Ponka
Keyword(s):  
Sequence Similarity ◽  
Erythroid Differentiation ◽  
Polyadenylation Signal ◽  
Erythroid Cell ◽  
Erythroid Cells ◽  
Erythroleukemia Cells ◽  
Haem Biosynthesis ◽  
Polyadenylation Sites ◽  
Dna Fragment ◽  
Polyadenylation Signals

Ferrochelatase, which catalyses the last step in haem biosynthesis, i.e. the insertion of Fe(II) into protophorphyrin IX, is present in all cells, but is particularly abundant in erythroid cells during haemoglobinization. Using mouse ferrochelatase cDNA as a probe two ferrochelatase transcripts, having lengths of 2.9 kb and 2.2 kb, were found in extracts of mouse liver, kidney, brain, muscle and spleen, the 2.9 kb transcript being more abundant in the non-erythroid tissues and the 2.2 kb transcript more predominant in spleen. In mouse erythroleukemia cells the 2.9 kb ferrochelatase transcript is also more abundant; however, following induction of erythroid differentiation by dimethyl sulphoxide there is a preferential increase in the 2.2 kb transcript, which eventually predominates. With mouse reticulocytes, the purest immature erythroid cell population available, over 90% of the total ferrochelatase mRNA is present as the 2.2 kb transcript. Since there is probably only one mouse ferrochelatase gene, the occurrence of two ferrochelatase transcripts could arise from the use of two putative polyadenylation signals in the 3′ region of ferrochelatase DNA. This possibility was explored by using a 389 bp DNA fragment produced by PCR with synthetic oligoprimers having sequence similarity with a region between the polyadenylation sites. This fragment hybridized only to the 2.9 kb ferrochelatase transcript, indicating that the two transcripts differ at their 3′ ends and suggesting that the 2.2 kb transcript results from the utilization of the upstream polyadenylation signal. The preferential utilization of the upstream polyadenylation signal may be an erythroid-specific characteristic of ferrochelatase gene expression.

Antagonistic Roles of ERK1/2 and p38 MAP Kinases in Hemoglobin Synthesis.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 3636-3636
Author(s):  
Volker Blank ◽  
Damien Lehalle ◽  
Louay Mardini ◽  
Mansouria Merad Boudia ◽  
Anna Derjuga ◽  
...  
Keyword(s):  
Map Kinases ◽  
Erythroid Differentiation ◽  
Mapk Signaling ◽  
Mitogen Activated Protein Kinase ◽  
Erythroid Cells ◽  
Differentiation Potential ◽  
P38 Inhibitor ◽  
Protein Levels ◽  
Molecular Events ◽  
Murine Erythroleukemia

Abstract Murine erythroleukemia (MEL) cells provide a valuable model to study the molecular events leading to erythroid differentiation. Maturing erythroid cells synthesize large quantities of hemoglobin, a process requiring the coordinated synthesis of heme and globin. Here, we investigated the role of the ERK and p38 mitogen-activated protein kinase (MAPK) signaling pathways in the differentiation of MEL cells. We determined the effect of the MEK1/2 inhibitor U0126 that blocks the ERK1/2 pathway, and the p38 inhibitor SB202190 on the differentiation potential of MEL cells induced by hexamethylene bisacetamide (HMBA). We found that treatment of HMBA induced MEL cells with the ERK1/2 pathway inhibitor U0126 results in higher hemoglobin levels. Using a fluorometric assay, we determined that intracellular heme levels also increased. Immunoblot studies showed an increase in globin protein levels. In contrast, treatment of MEL cells with the p38 inhibitor SB202190 has the opposite effect, leading to decreased amounts of heme and hemoglobin. In addition, inhibition of the p38 pathways results in lower transferrin receptor levels. Our results suggest that the ERK1/2 and p38 pathways play antagonistic roles in HMBA induced erythroid differentiation in MEL cells. This data also provides a novel link between MAPK signaling and the regulation of heme biosynthesis and iron uptake in erythroid cells.

Regulation of Erythropoiesis by Histone Methyltransferase EZH2 Inhibitor 3-Deazaneplanocin A (DZNep)

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 982-982
Author(s):  
Tohru Fujiwara ◽  
Haruka Saitoh ◽  
Yoko Okitsu ◽  
Noriko Fukuhara ◽  
Yasushi Onishi ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Target Genes ◽  
Conflicts Of Interest ◽  
K562 Cells ◽  
Erythroid Differentiation ◽  
Erythroid Cell ◽  
Mrna Levels ◽  
Wide Range ◽  
The Impact ◽  
Chip Analysis

Abstract Abstract 982 Background. EZH2, a core component of Polycomb repressive complex 2 (PRC2), plays a role in transcriptional repression through mediating trimethylation of histone H3 at lysine 27 (H3K27), and is involved in various biological processes, including hematopoiesis. Overexpression of EZH2 has been identified in a wide range of solid tumors as well as hematological malignancies. Recent studies indicated that 3-deazaneplanocin A (DZNep), an inhibitor of EZH2, preferentially induces apoptosis in cancer cells, including acute myeloid leukemia and myelodysplastic syndromes, implying that EZH2 may be a potential new target for epigenetic treatment. On the other hand, whereas PRC2 complex has been reported to participate in epigenetic silencing of a subset of GATA-1 target genes during erythroid differentiation (Yu et al. Mol Cell 2009; Ross et al. MCB 2012), the impact of DZNep on erythropoiesis has not been evaluated. Method. The K562 erythroid cell line was used for the analysis. The cells were treated with DZNep at doses of 0.2 and 1 microM for 72 h. Quantitative ChIP analysis was performed using antibodies to acetylated H3K9 and GATA-1 (Abcam). siRNA-mediated knockdown of EZH2 was conducted using Amaxa nucleofection technology™ (Amaxa Inc.). For transcription profiling, SurePrint G3 Human GE 8 × 60K (Agilent) and Human Oligo chip 25K (Toray) were used for DZNep-treated and EZH2 knockdown K562 cells, respectively. Gene Ontology was analyzed using the DAVID Bioinformatics Program (http://david.abcc.ncifcrf.gov/). Results. We first confirmed that DZNep treatment decreased EZH2 protein expression without significantly affecting EZH2 mRNA levels, suggesting that EZH2 was inhibited at the posttranscriptional level. We also confirmed that DZNep treatment significantly inhibited cell growth. Interestingly, the treatment significantly induced erythroid differentiation of K562 cells, as determined by benzidine staining. Transcriptional profiling with untreated and DZNep-treated K562 cells (1 microM) revealed that 789 and 698 genes were upregulated and downregulated (> 2-fold), respectively. The DZNep-induced gene ensemble included prototypical GATA-1 targets, such as SLC4A1, EPB42, ALAS2, HBA, HBG, and HBB. Concomitantly, DZNep treatment at both 0.2 and 1 microM upregulated GATA-1 protein level as determined by Western blotting, whereas the effect on its mRNA levels was weak (1.02- and 1.43-fold induction with 0.2 and 1 microM DZNep treatment, P = 0.73 and 0.026, respectively). Furthermore, analysis using cycloheximide treatment, which blocks protein synthesis, indicated that DZNep treatment could prolong the half-life of GATA-1 protein, suggesting that DZNep may stabilize GATA-1 protein, possibly by affecting proteolytic pathways. Quantitative ChIP analysis confirmed significantly increased GATA-1 occupancy as well as increased acetylated H3K9 levels at the regulatory regions of these target genes. Next, to examine whether the observed results of DZNep treatment were due to the direct inhibition of EZH2 or hitherto unrecognized effects of the compound, we conducted siRNA-mediated transient knockdown of EZH2 in K562 cells. Quantitative RT-PCR analysis demonstrated that siRNA-mediated EZH2 knockdown had no significant effect on the expression of GATA-1 as well as erythroid-lineage related genes. Furthermore, transcription profiles of the genes in the quantitative range of the array were quite similar between control and EZH2 siRNA-treated K562 cells, with a correlation efficient of 0.977. Based on our profiling results, we are currently exploring the molecular mechanisms by which DZNep promotes erythroid differentiation of K562 cells. Conclusion. DZNep promotes erythroid differentiation of K562 cells, presumably through a mechanism not directly related to EZH2 inhibition. Our microarray analysis of DZNep-treated K562 cells may provide a better understanding of the mechanism of action of DZNep. Disclosures: No relevant conflicts of interest to declare.

Fam210b Is Required for Optimal Cellular and Mitochondrial Iron Uptake during Erythroid Differentiation

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 405-405
Author(s):  
Yvette Y Yien ◽  
Caiyong Chen ◽  
Jiahai Shi ◽  
Liangtao Li ◽  
Daniel E. Bauer ◽  
...  
Keyword(s):  
Iron Uptake ◽  
Iron Transport ◽  
Aminolevulinic Acid ◽  
Genetic Modifier ◽  
Terminal Differentiation ◽  
Erythroid Differentiation ◽  
Hemoglobin Synthesis ◽  
Heme Synthesis ◽  
Mitochondrial Iron ◽  
Murine Erythroleukemia

Abstract Red cells synthesize large quantities of heme during terminal differentiation. Central to erythropoiesis is the transport and trafficking of iron within the cell. Despite the importance of iron transport during erythroid heme synthesis, the molecules involved in intracellular trafficking of iron are largely unknown. In a screen for genes that are up-regulated during erythroid terminal differentiation, we identified FAM210B, a predicted multi-pass transmembrane mitochondrial protein as an essential component of mitochondrial iron transport during erythroid differentiation. In zebrafish and mice, Fam210b mRNA is enriched in differentiating erythroid cells and liver (fetal and adult), which are tissues that require large amounts of iron for heme synthesis. Here, we report that FAM210B facilitates mitochondrial iron import during erythroid differentiation and is essential for hemoglobin synthesis. Zebrafish are anemic when fam210b is silenced using anti-sense morpholinos (Fig. A). CRISPR knockout of Fam210b caused a heme synthesis defect in differentiating Friend murine erythroleukemia (MEL) cells. PPIX levels in Fam210b deficient cells are normal, demonstrating that Fam210b does not participate in synthesis of the heme tetrapyrrole ring. Consistent with this result, supplementation of Fam210b deficient MEL cells with either aminolevulinic acid, the first committed substrate of the heme synthesis pathway or a chemical analog of protoporphyrin IX failed to chemically complement the heme synthesis defect. While Fam210b was not required for basal housekeeping heme synthesis, Fam210b deficientcells showed defective total cellular and mitochondrial iron uptake during erythroid differentiation (Fig. B). As a result, Fam210b deficient cells had defective hemoglobinization. Supplementation of Fam210b-/- MEL cells with non-transferrin iron chelates restored erythroid differentiation and hemoglobin synthesis; whereas, similar chemical complementation could not be achieved in the Tmem14c-/- cells, which have a primary defect in tetrapyrrole transport. (Fig. C). Our findings reveal that FAM210B is required for optimal mitochondrial iron import during erythroid differentiation for hemoglobin synthesis. It may therefore function as a genetic modifier for mitochondriopathies, anemias or porphyrias. Figure 1. Figure 1. Disclosures Bauer: Biogen: Research Funding; Editas Medicine: Consultancy. Orkin:Editas Inc.: Consultancy.

Sign in / Sign up

Export Citation Format

Share Document